Test Chamber Terminology

Change Rate/Ramp Rate:
rate at which environmental chamber heats up or cools down.

Device Under Test (DUT):
Product that will be tested in the chamber.

Live Load:
Any mass that is in the test chamber that produces heat. Live load could be electrical, mechanical, chemical, air purge or a continuous product process. This is used to size the correct refrigeration system for your chamber.

Dead Load:
Any mass that is in the test chamber that does not produce added heat. This is used to size the correct refrigeration system for your chamber.

Relative Humidity (RH):
The amount of water in an amount of air at a given temperature as compared to the maximum water that the air can hold at that same temperature.

Absolute Humidity:
The amount of water vapor in the air, typically expressed in grains/lb or water/lb.

Dry Bulb Temperature:
The temperature of a given sample of air.

Wet Bulb Temperature:
The temperature that results when water evaporates and cools a sensor.

Dew Point Temperature:
The temperature at which moisture will condense on a surface.

Air Velocity:
The speed of air.

Air Volume:
The amount of air.

Average Air Flow:
Chamber may pull down or heat up in temperature at different rates. It may be fast at the high end and slow at the low end. This is the standard air flow design used in most chambers.

Linear Air Flow:
Consistent rate of change at each temperature.

Chamber Operating Environment:
The external conditions at which the test chamber will be exposed to such as temperature, humidity, etc.

Transfer Time:
The amount of time it takes for an object to be moved from one chamber to another in thermal shock applications.

Upstream Recovery Time:
Also called “downstream recovery time,” this is the time required for the air temperature to recover in the new zone. Upstream recovery time can be measured in the air stream prior to or following the test load.

Control Tolerance:
The Temperature Controller uses a RTD control sensor, which is located in the discharge airflow. Control tolerance is a measure of how much the temperature varies after stabilization at the control sensor. It is a measure of the relative variations, NOT the absolute accuracy of the readout. The control tolerance specification for this chamber is ±1°C, or a total of 2°C. For example, the temperature set point may be -65.0°C. The actual temperature varies between -64°C and -66°C. These specifications are for an empty chamber. Tighter tolerances may be achieved across different temperature ranges. The addition of a test sample may effect the control variations. In some instances, the test sample will reduce these variations.

Uniformity:
Also known as Gradients. This is a measure of variations in temperature at different locations throughout the chamber interior, at the same time, after stabilization. The uniformity specification for this chamber is ±1°C or a total of 2°C, when measured at least 2" away from the chamber interior walls. These specifications are for an empty chamber. The addition of a test sample may effect the temperature uniformity. For example, an energized test sample will produce a higher temperature near the sample.

Controller Accuracy:
This is the ability of the temperature controller to accurately display a temperature measurement when compared to a standard. The controller display accuracy is ±0.65°C, ±1 LSD. However, the total measurement accuracy in the chamber includes the thermocouple sensor wire accuracy. RTD wire accuracy is ±1°C or 0.75% of reading, whichever is greater. Therefore, total system accuracy over the chamber’s typical operating range is typically ±1.65°C, ±1 LSD. This is not a measurement of chamber performance.

Frequency:
The rate of movement, measured in cycles, of a wave within a set time frame, usually one second. Frequency is often measured in hertz (Hz), which equals one wave cycle per second.